Pentair Minimax 400 questions

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Knj316

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Aug 3, 2011
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Hello everyone,

I want to start off by saying this board has been a great reference since my wife and I bought our first house a couple years ago. The house came with a large, 45' x 20' inground pool and spill over spa and we knew very little about pool care prior to taking ownereship. It's been a fair amount of work, but, worth it.

I'm hoping someone can point me in the right direction to troubleshoot our Pentair Minimax 400 Millivolt heater. When i run the heater, it will run for about 5 minutes or so, the heater turns off, the service LED becomes lit, then, goes out, and the heater comes on again. It will keep doing this until the water reaches the correct temperature.

It did this when we first moved in. I called the home warranty company who sent out a Pentair service tech who said the issue was likely due to an undersized gas meter. I had the gas company come out and replace the meter with a larger unit which didn't fix the issue. The Pentair tech came back and replaced the flow valve because it was badly corroded; this fixed problem up until recently.

I checked the flow valve and it looked fine; almost new. I also removed the service panels and made sure everything was cleaned out and all electrical connections were good. Does anyone have any suggestions i could try? I'm comfortable with safely working on this heater and replacing components, I just need to know what to check.

Thanks,

Joe
 
Thank you for the reply. I did take the "flow valve" out, which looks somewhat like a copper or bronze thermostat on a car and is installed in the water in/out headers on the heater and it looked fine - I didn't see much that could require cleaning. The other one was replaced because the pool chemistry had been bad at some point before we took ownership (home was foreclosure) and literally disintegrated.

Is the flow switch something different? I could try replacing the flow valve, but, I would need to purchase one at $100.00 or so.

Joe
 
We have a Minimax 400 as well, and I can tell you that these heaters need a properly sized gas line to work. When we purchased our house and got the pool running, the heater would not start. I called out a pool guy who first thought it was spider webs clogging the burners. But, after much trial and error, he tested the pressure on the gas line and found it to be quite low. It was keeping the heater from lighting up. So, we had to replace the gas line which was corroding. It was also undersized at 1". We ended up having it replaced with a 1 1/2" PE line, which was expensive. But, now the heater works without a hitch.

As others have said, it would be worth checking the pressure valve on the heater. But, also do a pressure test to make sure there is enough NG coming through the line.
 
Thanks for the suggestions. I will check the pressure valve sometime this weekend and hopefully be able to resolve the issue. Fortunately for us, we already had 1.5" gas piping going to the pool heater and the gas pressure has been fine since switching out the gas meter.
 
I've got a Minimax 400 that's been pretty reliable over the years (8+). However, recently my spa has stopped producing bubble when the pump is running. I'm thinking that maybe the heater is plugged, or the flow valve is malfunctioning. Can anyone describe what that flow valve (spring, copper "thermostat" looking thing) actually does? Is there any way to test it?
 
contraption said:
I've got a Minimax 400 that's been pretty reliable over the years (8+). However, recently my spa has stopped producing bubble when the pump is running. I'm thinking that maybe the heater is plugged, or the flow valve is malfunctioning. Can anyone describe what that flow valve (spring, copper "thermostat" looking thing) actually does? Is there any way to test it?
Click to expand...
I doubt the heater has anything to do with it. All it does is warm the water.

Somewhere there's an air intake that's connected to a type of venturi, that adds air and hence bubbles to the spa. Mine looks like an uncapped pipe with an elbow on it. There's probably some leaves or spider webs, something, blocking it. No air gets in, no bubbles.

Find the air intake, and run a plumber's snake down it. Or a drain king.
 
Richard320 said:
contraption said:
I've got a Minimax 400 that's been pretty reliable over the years (8+). However, recently my spa has stopped producing bubble when the pump is running. I'm thinking that maybe the heater is plugged, or the flow valve is malfunctioning. Can anyone describe what that flow valve (spring, copper "thermostat" looking thing) actually does? Is there any way to test it?
Click to expand...
I doubt the heater has anything to do with it. All it does is warm the water.

Somewhere there's an air intake that's connected to a type of venturi, that adds air and hence bubbles to the spa. Mine looks like an uncapped pipe with an elbow on it. There's probably some leaves or spider webs, something, blocking it. No air gets in, no bubbles.

Find the air intake, and run a plumber's snake down it. Or a drain king.
Click to expand...
To add to that, those venturi require a certain amount of (water)flow to properly pull the air in as well. check and make sure all your pump baskets are clear of debris and no excessive pressure on the filter gauge!
 
thanks guys. the top of my venturi (with blower on top) is clear but maybe there's something down inside, so i'll check again. As Richard320 suggested, I'm thinking that the low bubble problem is a symptom of low flow, but i can't seem to find any restriction. I've check the JVAs, T-cell, pump, and run the filter without cartridges. I've also replaced the (thankfully serviceable) check valve innards over on the spa makeup circuit. The only things left are 1 inline (glued in) check valve that i can't inspect, the heater, a weak pump, or some line restriction. The funny thing is that the pressure is running about normal, maybe a couple of psi higher than when it was built 8 years ago, but nothing major.

I just replaced the impeller and diffuser on the pump, but that didn't change anything. Has anyone ever seen a motor (3HP whisperflo) go "soft" where it can't pump like it used to? Would a failed or failing run capacitor affect the motor power?

The pump did pop the breaker for the very first time a few days ago and would struggle to start afterward. For a week or so before that, the bubbles were decreasing day by day. when I took the pump apart I did find that the impeller seemed a little bit stuck with some small, tough, leaves stuck in the small gap between the impeller nose and the diffuser ring. I replaced both parts (i had the parts on hand as i've been thinking this problem might be "blow by" inside the pump), but as I said, no luck there. It is at least running again, but still no bubbles.

I'm usually really good at detective work like this, but this one has me flummoxed.

Do check valves get stuck (this one is after the filter)? Motors go soft? Heaters get clogged?
 

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Yes, check valves can and do get stuck. The flow control "flap" type tend to tear the rubber mount off causing the disk to block the outlet port.

On a 3hp pump, If the pressure is over 30, there difference between it flowing, and not could only be 8 psi,
 
@racket: regarding the check valve - is there any way to figure out if the flapper is busted? it appears to be a sealed "capsule". The other one I have (spa makeup) has a screw-on lid and replaceable spring loaded assembly inside (that i've replaced). It seems like i might need a snake style inspection camera to get inside the capsule one. In your experience, is failure likely after 8 years of service?

My pressure with only the main pump on (no solar) runs about 22-24psi with clean cartridges. It's always been higher with the spa on, maybe 30 or 32 psi. It might be a bit higher than that now, but not as high as I imagine it would go if the pump were deadheaded.
 
contraption said:
It seems like i might need a snake style inspection camera to get inside the capsule one. In your experience, is failure likely after 8 years of service?.
Click to expand...

The only way I know would be to tap in a pressure gauge on the effluent (outlet) side of the check valve. Instead of worrying about renting a camera to inspect it, I would replace it with a Pentair or Jandy check valve with replaceable internals.
 
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